Hello @CocoP24 ,
I was able to check out the ad in your campaigns, and was able to successfully save the edit I made. I'm wondering if there's a connection or caching issue or something similar preventing the save from going through on your end. Would you be able to try some of the following connectivity troubleshooting steps, to see if they alleviate the issue?
Otherwise you could try recreating the ad from scratch to see if it lets you through then. Please let us know if any of these methods allow you to save your design edits.